We have studied a total of 25 patients with metastatic colon or appendiceal adenocarcinoma. All patients received I-131 B72.3 intraperitoneally. In addition selected patients were co-infused with a control antibody to determine the specificity of localization. In other cases the patients were co-injected with I-125 B72.3 intravenously to determine which was the better route. We have documented tumor specific uptake. We have also documented that there is preferential targeting of peritoneal implants by the intraperitoneal route compared to the intraperitoneal route. Most patients receiving intraperitoneal antibody developed human antimouse antibodies.